<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
    a:link{
        color: burlywood;
    }
    a:visited{
        color: midnightblue;
    }
    div{
        width: 200px;
        height: 200px;
        background: navy;
    }
    div:hover{
        background: orangered;
    }
    div:active{
        background: orchid;
    }
    p:before{
        content: "H";
    }
    h4::after{
        content: "ld!";
    }
    </style>
</head>
<body>
    <a href="http://www.baidu.com" target="_blank">这是一个a标签</a>
    <div></div>
    <p>ello world!</p>
    <p>123</p>
    <p>1231</p>
    <h4>Hello wor</h4>
</body>
</html>